A typical magnetic disc drive includes one or more read/write heads for reading data from or writing data to one or more discs mounted on a spindle motor. The data is stored in generally concentric tracks on the disc surfaces. During drive operations, the read/write heads are positioned at selected radial locations while the discs are rotated by the spindle motor. Rotary actuators are often employed to carry the read/write heads to the desired locations. The actuator is coupled to a voice coil motor which provides the torque for rotating the actuator about its pivot. Ball bearing pivots are typically chosen for their compactness. However, ball bearings operate with some degree of pre-load and friction, which can lead to non-linearity in the movement of the actuator.
Flexural pivots appear to offer a feasible alternative to ball bearing pivots in that there is no stiction and that the resolution of positioning can be essentially a function of the servo control system. Attempts have been made in the past to incorporate flexural pivots into disc drives, such as the pivot systems described in the U.S. Pat. No. 5,504,641, issued to Diel on Apr. 2, 1996, and the U.S. Pat. No. 5,029,030, issued to Luecke on Jul. 2, 1991. However, these designs include large, unwieldy springs which are unsuitable in modern disc drives where size is an important consideration.
General purpose flexural pivots have also been designed, such as those of the type described in U.S. Pat. No. 3,811,665, issued to Seelig on May 21, 1974. In such flexural pivots, two flat springs are assembled so that a solid center of one spring is disposed within an open center of the other spring. The springs are coupled at their longitudinal edges to undercut slots inside a circular sleeve. Such flexural pivots can be difficult to assemble, however, and no pivots of this type have been successfully incorporated into disc drives. There remains therefore a need for an improved flexural pivot for use with a rotary actuator, one which eliminates the problems associated with conventional ball bearing cartridges while being suitable for use in modern disc drives.